Optical semiconductor device having photosensitive diodes and process for fabricating such a device

ABSTRACT

An optical semiconductor device includes, in a zone ( 5 ), a structure of photosensitive diodes including a matrix ( 6 ) of lower electrodes ( 7 ), an intermediate layer ( 9 ) made of a photosensitive material formed on the matrix of lower electrodes and at least one upper electrode ( 10   a ) formed on the intermediate layer, in which an electrical connection ( 3   a ) includes at least one electrical contact pad ( 7   a ) and at least one electrical connection pad ( 16   a ) are produced beneath the intermediate layer, at least one electrical connection via ( 14 ) is produced through the intermediate layer and connects the upper electrode to the electrical contact pad and at least one well ( 15   a ) is formed outside the zone ( 5 ) and passes through at least the intermediate layer ( 9 ) in order to expose the electrical connection pad ( 16   a ). Also provided is a process for fabricating such a device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims priority from prior FrenchPatent Application No. 05 00408, filed on Jan. 14, 2005, the entiredisclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of optical semiconductordevices, and more particularly to an optical semiconductor device havinga structure of photosensitive diodes.

2. Description of the Related Art

U.S. Pat. No. 6,455,836 discloses a photosensitive semiconductor devicethat comprises, on top of a base layer, an intermediate layer made of aphotosensitive material, projecting lower electrodes in this layer andan upper layer that includes an upper electrode. A lateral well passesthrough the intermediate layer and the upper layer. The base layerincludes connection means that are connected selectively to the lowerelectrodes and comprise connection pads placed in the bottom of theaforementioned well. A local layer made of an electrically-conductivenon-transparent material covers some of the diodes in order to form anoptical barrier and extends along the sidewalls and in the bottom of thewell so as to electrically connect the upper electrode to the electricalconnection pads. Such an arrangement is not suitable for implementationon standard fabrication machines, especially planarization machines, andrequires a tricky final operation to produce the local layer.

Accordingly, there exists a need for overcoming the disadvantages of theprior art as discussed above.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides an optical semiconductordevice comprising photosensitive diodes of simplified structure andsimplified fabrication.

The first subject of the present invention is a semiconductor devicecomprising, in a zone, a structure of photosensitive diodes comprising amatrix of lower electrodes, an intermediate layer made of aphotosensitive material formed on the matrix of lower electrodes, and atleast one upper electrode formed on the intermediate layer.

According to the invention, the device comprises, beneath theintermediate layer, electrical connection means that include at leastone electrical contact pad and at least one electrical connection pad.

According to the invention, the device comprises at least one electricalconnection via passing through at least the intermediate layer andconnecting the upper electrode to the electrical contact pad.

According to the invention, the device has at least one well formedoutside the zone and passing through at least the intermediate layer,this well exposing the electrical connection pad.

According to the invention, the device preferably comprises a lowerdielectric layer in which the matrix of lower electrodes and the atleast one electrical contact pad are formed and, beneath this lowerlayer, a base layer in which the at least one electrical connection padis formed, the at least one well passing through this lower layer inorder to expose this electrical connection pad.

According to the invention, the device preferably includes an upperlayer comprising a first layer constituting the second electrode and asecond layer made of an electrically conductive material, the at leastone via and the at least one well passing through this upper layer.

According to the invention, the device preferably includes anon-transparent local layer that partly covers the structure ofphotosensitive diodes.

According to the invention, the local layer is preferably made of anelectrically conductive material, the at least one via being connectedto this local layer.

According to the invention, the device preferably includes at least onetransparent outer protective layer.

Another subject of the present invention is a process for fabricating anoptical semiconductor device comprising a multiplicity of photosensitivediodes comprising lower electrodes and at least one upper electrode thatare separated by an intermediate layer made of a photosensitivematerial.

According to the invention, this process consists of: producing a baselayer that includes electrical connection means; forming a dielectriclower layer above the base layer; forming, in the lower layer, a matrixof lower electrodes that are selectively connected to the electricalconnection means; producing an intermediate layer made of aphotosensitive material on the lower layer; forming an upper layer madeof an electrically conductive transparent material; forming at least onevia made of an electrically conductive material through the intermediateand upper layers so as to electrically connect the upper layer and atleast one of the lower electrodes; and producing at least one wellthrough the lower, intermediate and upper layers so as to expose atleast one electrical connection pad of the electrical connection means,the at least one electrical connection pad being connected to the atleast one via.

According to the invention, the at least one via is preferably producedabove the corresponding lower electrode.

According to the invention, the process preferably consists in formingan upper layer comprising a first layer made of a first electricallyconductive material and a second layer made of a second electricallyconductive material.

According to the invention, the process preferably consists in forming alocal layer made of a non-transparent material above the upper layer andextending partly above the multiplicity of photosensitive diodes.

According to the invention, the process preferably consists in forming aprotective outer layer made of a transparent material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from studying theoptical semiconductor devices having photosensitive diodes that aredescribed by way of non-limiting examples and illustrated schematicallyby the drawing in which:

FIG. 1 shows a sectional view of an optical semiconductor deviceaccording to the invention;

FIG. 2 shows a top view of the device of FIG. 1;

FIG. 3 shows a first step in the fabrication of the device of FIG. 1, ina sectional view;

FIG. 4 shows a top view of FIG. 3;

FIG. 5 shows a second step on the fabrication of the device of FIG. 1,in a sectional view;

FIG. 6 shows a third step in the fabrication of the device of FIG. 1, ina sectional view;

FIG. 7 shows a fourth step in the fabrication of the device of FIG. 1,in a sectional view;

FIG. 8 shows a sectional view of an alternative embodiment of the deviceof FIG. 1; and

FIG. 9 shows a sectional view of another alternative embodiment of thedevice of FIG. 1.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, these show a semiconductor device 1 in thefinal state.

This device 1 comprises a dielectric base layer 2 that includeselectrical connection means 3 flush with its surface and, on this baselayer, a dielectric lower layer 4.

This lower layer 4 includes, in a zone 5, a matrix 6 of lower electrodes7 that are flush with its surface and are selectively connected to theelectrical connection means 3 by electrical connections vias 8. Thelower electrodes 7 may in particular be made of chromium or n-dopedsilicon.

The device 1 includes, on the lower layer 4, an intermediate layer 9made of a photosensitive material which may in particular be amorphousor polycrystalline silicon.

The device 1 includes, on the intermediate layer 9, a transparent upperlayer 10 formed by a first layer 10 a of a first electrically conductivematerial, constituting an upper electrode, and a second layer 10 b madeof a second electrically conductive material. The first layer 10 a mayin particular be p-doped silicon and the second layer 10 b may inparticular be ITO (indium tin oxide).

The device 1 includes, on the intermediate layer 10, an insulatingtransparent outer protective layer 11.

The device 1 includes, on the outer layer 11, a non-transparent locallayer 12 that, in the example, extends in the form of a ring coveringthe lower electrodes of two or three outer rows of the matrix 6. Thislocal layer 12 may in particular be made of a metal of the Al or Ti/TiNtype.

The device 1 has holes 13 that extend through the aforementioned layers9, 10 and 11, between the local layer 12 and the lower electrodes 7 a ofthe outer row of the matrix 6 of lower electrodes. These holes arefilled with an electrically conductive material, for example copper,constituting vias 14 for electrically connecting the layer 10 by lateralcontact to the lower electrodes 7 a that constitute electricalconnection pads. The local layer 12 extends or passes over the vias 14and so is connected to these vias and to the branch 3 a through thesevias.

Advantageously, the local layer 12 and the vias 14 can be made with thesame material. They can be realized in a single step of the process.

It follows from the foregoing that, with the exception of the peripheralzone corresponding to the vias 14 associated with the lower electrodes 7a, the device 1 has a structure 6 a of photosensitive diodes formedbetween the remaining lower electrodes 7 b and the upper electrode 10 a.The photosensitive diodes located facing the central aperture in thelocal annular layer 12 are sensitive to the external light, while thephotosensitive diodes located beneath this non-transparent local annularlayer 12 are not sensitive thereto.

Outside the zone 5, and therefore outside the local annular layer 12,the device 1 has a multiplicity of wells 15 distributed around itsperiphery, which pass through the layers 4, 9, 10 and 11. These wellsexpose electrical connection pads 16 that are selectively connected tothe electrical connection means 3.

In particular, a well 15 a exposes an electrical connection pad 16 athat is exclusively connected to the electrodes 7 a, and therefore tothe upper electrode 10, by the intermediary of the vias 14 and of abranch 3 a.

The device 1 can be connected to any other electrical or electronicmeans by the intermediary of electrical connection wires 17, the ends ofwhich are respectively introduced into the wells 15 and bonded to thecorresponding electrical connection pads.

One method of fabricating the semiconductor device 1 described above,employing known techniques, especially etching, deposition andplanarization, will now be described with reference to FIGS. 3 to 8.

As FIGS. 3 and 4 show, after the connection means 3 have been producedin the base layer 2 and its surface has been planarized, the processcontinues with the deposition of the upper layer 4. The vias 8 areproduced, and then the matrix 6 of lower electrodes 7.

As FIG. 5 shows, after the surface of the layer 4, including the vias 8and the lower electrodes 7, have been planarized, the process continueswith the deposition of the intermediate layer, of the layer 10, bysuccessively depositing its first layer 10 a and its second layer 10 b,and of the outer layer 11, optionally with intermediate planarizationoperations being carried out.

As FIG. 6 shows, holes 13 are produced through the layers 9, 10 and 11,down to just above the peripheral lower electrodes 7 a.

As FIG. 7 shows, the vias 14 are then produced, followed by the locallayer 12.

Finally, the wells 15 are produced through the layers 4, 9, 10 and 11down to the connection pads 16 so as to finally obtain the device asshown in FIGS. 1 and 2.

As shown in FIGS. 2 and 4, preferably several devices 1 located besideone another are produced on a common base layer 2, by carrying out theaforementioned operations jointly. Each individual device 1 is thenproduced, for example by sawing.

Referring to FIG. 8, it may be seen that, according to an alternativeembodiment, it would optionally be possible to deposit an additionaltransparent outer protective layer 11 a on the front of the outer layer10 and of the local layer 12.

Referring to FIG. 9, this shows that, according to another alternativeembodiment, it would be possible to form the vias 14 through the layers9 and 10, to form the local layer 12 on the upper layer 10 and thenoptionally to form the outer protective layer 11 on the front of thisupper layer 10 and of this local layer 12.

The present invention is not limited to the examples described above.

In particular, the local layer 12 does not go right around the matrix 6but, for example, it could be limited to one side of this matrix. Thenumber of vias 14 could be reduced, and these vias could be providedonly around part of the periphery of the matrix 6. Many otheralternative embodiments are possible without departing from theframework defined by the appended claims.

While there has been illustrated and described what is presentlyconsidered to be embodiments of the present invention, it will beunderstood by those of ordinary skill in the art that various othermodifications may be made, and equivalents may be substituted, withoutdeparting from the true scope of the present invention.

Additionally, many modifications may be made to adapt a particularsituation to the teachings of the present invention without departingfrom the central inventive concept described herein. Furthermore, anembodiment of the present invention may not include all of the featuresdescribed above. Therefore, it is intended that the present inventionnot be limited to the particular embodiments disclosed, but that theinvention include all embodiments falling within the scope of theappended claims.

1. A semiconductor device comprising: in a zone, a structure ofphotosensitive diodes comprising: a matrix of lower electrodes; anintermediate layer made of a photosensitive material formed on thematrix of lower electrodes; and at least one upper electrode formed onthe intermediate layer, and wherein the semiconductor device comprises,beneath the intermediate layer, electrical connection means thatincludes at least one electrical contact pad and at least one electricalconnection pad, in that the semiconductor device includes at least oneelectrical connection via passing through at least the intermediatelayer and connecting the at least one upper electrode to the at leastone electrical contact pad, and in that the semiconductor device has atleast one well formed outside the zone and passing through at least theintermediate layer, this well exposing the electrical connection pad. 2.The device according to claim 1, including an upper layer comprising afirst layer constituting the second electrode and a second layer made ofan electrically conductive material, the at least one via and the atleast one well passing through this upper layer.
 3. The device accordingto claim 1, including a non-transparent local layer that partly coversthe structure of photosensitive diodes.
 4. The device according to claim3, wherein the local layer is made of an electrically conductivematerial, the at least one via being connected to this local layer. 5.The device according to claim 1, including at least one transparentouter protective layer.
 6. The device according to claim 1 furthercomprising: a lower dielectric layer in which the matrix of lowerelectrodes and the at least one electrical contact pad are formed and,beneath this lower layer, a base layer in which the at least oneelectrical connection pad is formed, the at least one well passingthrough this lower layer in order to expose this electrical connectionpad.
 7. The device according to claim 6, including an upper layercomprising a first layer constituting the second electrode and a secondlayer made of an electrically conductive material, the at least one viaand the at least one well passing through this upper layer.
 8. Thedevice according to claim 6, including a non-transparent local layerthat partly covers the structure of photosensitive diodes.
 9. The deviceaccording to claim 8, wherein the local layer is made of an electricallyconductive material, the at least one via being connected to this locallayer.
 10. The device according to claim 8, wherein the local layer andthe at least one via are in the same material.
 11. The device accordingto claim 6, including at least one transparent outer protective layer.12. A process for fabricating a semiconductor device comprising amultiplicity of photosensitive diodes comprising lower electrodes and atleast one upper electrode that are separated by an intermediate layermade of a photosensitive material, the process consisting of: producinga base layer that includes electrical connection means; forming adielectric lower layer above the base layer; producing, in the lowerlayer, a matrix of lower electrodes that are selectively connected tothe electrical connection means; producing an intermediate layer made ofa photosensitive material on the lower layer; forming an upper layermade of an electrically conductive transparent material; producing atleast one via made of an electrically conductive material through theintermediate and upper layers so as to electrically connect the upperlayer and at least one of the lower electrodes; and producing at leastone well through the lower, intermediate and upper layers so as toexpose at least one electrical connection pad of the electricalconnection means, the at least one electrical connection pad beingconnected to the at least one via.
 13. The process according to claim12, wherein the at least one via is produced above the correspondinglower electrode.
 14. The process according to claim 12, furtherconsisting of: forming an upper layer comprising a first layer made of afirst electrically conductive material and a second layer made of asecond electrically conductive material.
 15. The process according toclaim 12, further consisting of: forming a local layer made of anon-transparent material above the upper layer and extending partlyabove the multiplicity of photosensitive diodes and extending over theat least one via.
 16. The process according to claim 15, wherein thelocal layer and the at least one via are in the same material.
 17. Theprocess according to claim 12, further consisting of: forming an outerprotective layer made of a transparent material.